A high thermal conductivity, corona-resistant, electromagnetic shielding composite aramid insulation paper, preparation method and application thereof

Abstract

The invention discloses a high-thermal-conductivity, corona-resistant, and electromagnetic-shielding composite aramid insulation paper, a preparation method, and an application thereof, comprising the following steps: step 1: using meta-aramid fiber as a shell layer and carbon nanotubes as a core layer, and obtaining coaxial nanofiber yarns by coaxial electrostatic spinning; step 2: fully mixing mica nanosheets, fluorinated graphene, and meta-aramid fiber in a solvent to obtain a mixed slurry; step 3: preparing a nanofiber felt from the coaxial nanofiber yarns; step 4: using the nanofiber felt as an interlayer material and the mixed slurry as a surface material, and forming a multilayer structural material with the upper and lower surfaces of the interlayer material covered with the surface material by a vacuum filtration method; step 5: hot-pressing the multilayer structural material to obtain the desired composite aramid insulation paper; the aramid insulation paper obtained by the invention has excellent thermal conductivity, corona resistance, and electromagnetic shielding properties, and can meet the requirements of advanced power electronic devices and electrical equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating materials, and in particular to a high-thermal-conductivity, corona-resistant, electromagnetic-shielding composite aramid insulating paper, a preparation method and applications thereof. Background Art

[0002] Reliable insulation is the cornerstone of the safe and stable operation of ultra-high voltage transmission networks. The appropriate use of insulating materials with electromagnetic shielding capabilities in ultra-high voltage transformers, reactors, and other electrical equipment can optimize electric field distribution and significantly improve overall insulation effectiveness. Transformers are core equipment in power systems that perform important tasks such as voltage conversion and energy distribution. Improving their energy efficiency has a significant impact on the overall energy efficiency of the power system. In transformers, winding leakage flux enters the steel casing, generating significant eddy current losses, a major obstacle to further reducing transformer losses. High-performance electromagnetic shielding materials can effectively reduce this leakage flux, thereby reducing transformer eddy current losses. Furthermore, while the rapid development of electrical equipment and power electronics technology has promoted social progress, it has also led to increasingly serious electromagnetic interference (EMI) problems. This interference not only affects the normal operation of equipment but can also adversely affect the surrounding environment and other electronic equipment, necessitating effective shielding.

[0003] While the current development of advanced electrical equipment with higher power, higher frequency, and greater integration has brought numerous benefits and advancements to production and life, it has also led to serious issues such as heat accumulation and high-frequency corona discharge, posing significant safety risks to the stable and reliable operation of these devices. As an insulating medium widely used in electrical equipment such as motors, reactors, and bushings, the thermal conductivity, corona resistance, and mechanical strength of traditional insulation paper no longer meet the current demands of electrical equipment development. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a high-thermal-conductivity, corona-resistant, electromagnetic-shielding composite aramid insulation paper, a preparation method and an application thereof.

[0005] The technical solution adopted by the present invention is: a method for preparing high thermal conductivity and corona resistant electromagnetic shielding composite aramid insulation paper, comprising the following steps:

[0006] Step 1: Using meta-aramid fiber as the shell layer and carbon nanotubes as the core layer, coaxial nanofiber filaments are obtained by coaxial electrospinning;

[0007] Step 2: fully mixing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers in a solvent to obtain a mixed slurry; the mass ratio of the mica nanosheets, fluorinated graphene and meta-nano-aramid fibers is 0.1-0.3:0.1-0.2:1;

[0008] Step 3: preparing a nanofiber mat using the coaxial nanofibers obtained in step 1;

[0009] Step 4: Using the nanofiber mat obtained in step 3 as the interlayer material and the mixed slurry as the surface material, a multilayer structure material is formed by vacuum filtration, wherein the upper and lower surfaces of the interlayer material are covered with the surface material;

[0010] Step 5: hot-press the multilayer structure material obtained in step 4 to obtain the desired composite aramid insulation paper.

[0011] Furthermore, in step 1, the diameter of the coaxial nanofiber filament is 200-600 nm, and the ratio of the radius of the core layer to the thickness of the shell layer in the coaxial nanofiber filament is 2-5:8-5.

[0012] Furthermore, the meso-aramid fiber in step 1 needs to be pretreated before use:

[0013] Cutting the meta-aramid fiber into 5-10 mm short fibers;

[0014] The chopped fibers were ultrasonically treated in acetone, then vacuum filtered and rinsed three times, and then dried. After drying, the fibers were dissolved in a LiCl solution to obtain a meta-aramid fiber solution.

[0015] Furthermore, the preparation method of the mica nanosheets in step 2 is as follows:

[0016] adding mica powder to the intercalant solution and obtaining a mica dispersion after ultrasonic treatment;

[0017] The mica dispersion was heated at 100°C for 6 hours; after centrifugal rinsing, it was dried under vacuum conditions;

[0018] The preparation process of meta-nano-aramid fiber is as follows:

[0019] Cutting the meta-aramid fiber into 5-10 mm short fibers;

[0020] The chopped fibers were ultrasonicated in acetone, then rinsed three times by vacuum filtration and then dried;

[0021] The dried meta-aramid fiber is dissolved in a strong alkaline solution, fully stirred, and subjected to ultrasonic dispersion treatment.

[0022] Furthermore, the mixed slurry preparation process in step 2 is as follows:

[0023] Mica nanosheets and fluorinated graphene were added to the solvent dimethyl sulfoxide and ultrasonicated in a water bath;

[0024] adding meta-nano-aramid fiber dispersion;

[0025] Deionized water is dropped into the mixed solution, and the mixture is subjected to water bath ultrasonic treatment to obtain a mixed solution;

[0026] The mixed solution after ultrasonication was injected into deionized water to generate floccules;

[0027] The flocculants are dispersed in deionized water and sheared at high speed to obtain a dispersed and stable mixed slurry.

[0028] Furthermore, in step 4, the mass ratio of the surface layer material to the interlayer material is 7-9:3-1.

[0029] Furthermore, the hot pressing process in step 5 is as follows:

[0030] First, hot pressing was performed at a pressure of 12 MPa and a temperature of 180°C for 6 min;

[0031] Then, the pressure was maintained at 12 MPa at room temperature for 2 minutes.

[0032] A high thermal conductivity, corona resistance, electromagnetic shielding composite aramid insulation paper, the composite aramid insulation paper is a composite sandwich structure formed by hot pressing with an outer layer material covering the upper and lower surfaces of the sandwich material;

[0033] The sandwich material is a composite nanofiber felt prepared by coaxial nanofiber filaments obtained by coaxial electrospinning, with meta-aramid fiber as the shell layer and carbon nanotubes as the core layer;

[0034] The outer layer material is a mixed slurry obtained by fully mixing and dispersing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers.

[0035] Furthermore, the carbon nanotubes have a length of 0.4 to 5 μm and a diameter of 8 to 20 nm; the mica nanosheets have a particle size of 300 to 600 nm and a thickness of 100 to 200 nm; the fluorinated graphene has a single-layer structure, a fluorine-carbon ratio of 1:1, a particle size of 4 to 8 μm, and a thickness of 1 to 2 nm.

[0036] The invention discloses an application of high-thermal-conductivity, corona-resistant and electromagnetic-shielding composite aramid insulation paper, wherein the composite aramid insulation paper is used for preparing insulation components of power transformers.

[0037] The beneficial effects of the present invention are:

[0038] The composite aramid insulating paper obtained by the present invention has excellent thermal conductivity, corona resistance and electromagnetic shielding properties, and can meet the needs of advanced power electronic devices and electrical equipment for insulating media in various harsh application scenarios such as high temperature, high frequency pulses, strong electric fields, and electromagnetic sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1This is a schematic structural diagram of the composite aramid insulation paper obtained by the present invention.

[0040] Figure 2 Schematic diagram of the structure of the coaxial nanofiber filaments in the present invention.

[0041] Figure 3 This is a scanning electron microscope (SEM) image of the interlayer material obtained in step 4 of Example 1 of the present invention.

[0042] Figure 4 Schematic diagram comparing the breakdown strength of the composite aramid insulation paper obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0043] Figure 5 Schematic diagram comparing the corona resistance time of the composite aramid insulation paper obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0044] Figure 6 Schematic diagram comparing the electromagnetic shielding effectiveness of the composite aramid insulation paper obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0045] Figure 7 Schematic diagram comparing the thermal conductivity of the composite aramid insulation paper obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0046] Figure 8 Schematic diagram comparing the mechanical tensile strain-stress curves of the composite aramid insulation paper obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

[0047] In the figure: 1-outer layer material, 2-interlayer material, 3-meta-aramid fiber shell layer, 4-carbon nanotube core layer. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0049] A method for preparing high thermal conductivity, corona-resistant, electromagnetic shielding composite aramid insulation paper comprises the following steps:

[0050] Step 1: Using meta-aramid fiber as the shell layer and carbon nanotubes as the core layer, coaxial nanofiber filaments are obtained by coaxial electrospinning;

[0051] First, pre-treat the meta-aramid fiber:

[0052] Cutting the meta-aramid fiber into 5-10 mm short fibers;

[0053] The chopped fibers were ultrasonically treated in acetone, then vacuum filtered and rinsed three times, and then dried. After drying, the fibers were dissolved in a LiCl solution to obtain a meta-aramid fiber solution.

[0054] The carbon nanotubes have a length of 0.4 to 5 μm and a diameter of 8 to 20 nm. The coaxial nanofibers have a diameter of 200 to 600 nm, and the ratio of the core radius to the shell thickness of the coaxial nanofibers is 2 to 5:8 to 5. The diameter of the coaxial nanofibers and the ratio of the core radius to the shell thickness are controlled by controlling the electrospinning parameters and are set according to actual needs, as long as they are within this range.

[0055] Step 2: fully mixing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers in a solvent to obtain a mixed slurry; the mass ratio of the mica nanosheets, fluorinated graphene and meta-nano-aramid fibers is 0.1-0.3:0.1-0.2:1;

[0056] The preparation method of mica nanosheets is as follows:

[0057] adding mica powder to the intercalant solution and obtaining a mica dispersion after ultrasonic treatment;

[0058] The mica dispersion was heated at 100°C for 6 hours; after centrifugal rinsing, it was dried under vacuum conditions;

[0059] The preparation process of meta-nano-aramid fiber is as follows:

[0060] Cutting the meta-aramid fiber into 5-10 mm short fibers;

[0061] The chopped fibers were ultrasonicated in acetone, then rinsed three times by vacuum filtration and then dried;

[0062] The dried meta-aramid fiber is dissolved in a strong alkaline solution, fully stirred, and subjected to ultrasonic dispersion treatment.

[0063] The mica nanosheets have a particle size of 300 to 600 nm and a thickness of 100 to 200 nm; the fluorinated graphene has a single-layer structure with a fluorine-carbon ratio of 1:1, a particle size of 4 to 8 μm, and a thickness of 1 to 2 nm.

[0064] The mixed slurry preparation process is as follows:

[0065] Mica nanosheets and fluorinated graphene were added to the solvent dimethyl sulfoxide and ultrasonicated in a water bath;

[0066] adding meta-nano-aramid fiber dispersion;

[0067] Deionized water is dropped into the mixed solution, and the mixture is subjected to water bath ultrasonic treatment to obtain a mixed solution;

[0068] The mixed solution after ultrasonication was injected into deionized water to generate floccules;

[0069] The flocculants are dispersed in deionized water and sheared at high speed to obtain a dispersed and stable mixed slurry.

[0070] Step 3: preparing a nanofiber mat using the coaxial nanofibers obtained in step 1;

[0071] Step 4: Using the nanofiber mat obtained in step 3 as the interlayer material and the mixed slurry as the surface material, a multilayer structure material is formed by vacuum filtration, wherein the upper and lower surfaces of the interlayer material are covered with the surface material;

[0072] The mass ratio of the surface material to the interlayer material is 7-9:3-1.

[0073] Step 5: hot-press the multilayer structure material obtained in step 4 to obtain the desired composite aramid insulation paper.

[0074] The hot pressing process is as follows:

[0075] First, hot pressing was performed at a pressure of 12 MPa and a temperature of 180°C for 6 min;

[0076] Then, the pressure was maintained at 12 MPa at room temperature for 2 minutes.

[0077] Composite aramid insulation paper is a composite sandwich structure formed by hot pressing with outer layer materials on the upper and lower surfaces of the sandwich material. Figure 1 As shown;

[0078] The sandwich material is a composite nanofiber felt prepared by coaxial nanofiber yarns obtained by coaxial electrospinning with meta-aramid fiber as the shell layer and carbon nanotubes as the core layer; the coaxial nanofiber yarn structure is as follows Figure 2 shown.

[0079] The outer layer material is a mixed slurry obtained by fully mixing and dispersing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers.

[0080] Example 1

[0081] A method for preparing high thermal conductivity, corona-resistant, electromagnetic shielding composite aramid insulation paper comprises the following steps:

[0082] Step 1: Using meta-aramid fiber as the shell layer and carbon nanotubes as the core layer, coaxial nanofiber filaments are obtained by coaxial electrospinning;

[0083] First, pre-treat the meta-aramid fiber:

[0084] The meta-aramid fiber filaments were mechanically cut into chopped fibers with a length of 5 to 10 mm. The chopped fibers were then soaked in acetone and subjected to 300W water bath ultrasound for 72 hours to remove stains. After filtering out the acetone, the chopped fibers were soaked in anhydrous ethanol for 12 hours. Subsequently, the fibers were vacuum filtered and rinsed three times with anhydrous ethanol and then with deionized water. Finally, the rinsed fibers were vacuum dried at 60°C for at least 5 days for use.

[0085] Weigh 1.6 g of anhydrous LiCl and stir it thoroughly in 80 g of DMAc until it is completely dissolved. Weigh 20 g of pretreated meta-aramid fiber and add it to the solution. Seal and stir in an 80 °C water bath until a uniform transparent solution is formed. Finally, keep the prepared meta-aramid fiber solution sealed and place it at room temperature for 24 h to degas.

[0086] Preparation of carbon nanotube dispersion: 3 g of carbon nanotubes and 2 g of DMAc were weighed into a test tube, which was sealed with parafilm. Ultrasonication was performed in a 60 W water bath at room temperature until no visible precipitation was present at the bottom of the test tube and a stable Tyndall effect was observed when the dispersion was irradiated with laser.

[0087] An electrospinning needle was assembled using an 18G stainless steel needle (1.00mm inner diameter) as the outer needle and a 24G stainless steel needle (0.30mm inner diameter) as the inner needle. The carbon nanotube dispersion and meta-aramid fiber dispersion were each drawn into two 10mL syringes. The syringe containing the carbon nanotube dispersion was connected to the inner needle, and the syringe containing the meta-aramid fiber dispersion was connected to the outer needle, ensuring no dripping or leaking. Subsequently, the two syringes were placed in the syringe pump's push position. The electrospinning machine was powered on, with the distance between the spinning head and the drum receiver set to 15cm, the spinning voltage set to 18kV, the drum receiver speed set to 200rpm, the ambient temperature set to 25°C, and the humidity set to 40%RH. The injection rate for the syringe pump's inner needle was 0.10-0.15mL / h, and the injection rate for the outer needle was 0.45-0.60mL / h, ensuring that the liquid exited the needle without dripping or interrupting the spinning process.

[0088] After the electrospinning is completed, preliminary drying is performed to remove the incompletely volatilized DMAc solvent. The steps are as follows:

[0089] The coaxial aramid fiber yarn prepared by the coaxial spinning process was carefully peeled off from the receiver roller to avoid bending and breakage, and then spread on a glass plate and placed in a constant temperature vacuum drying oven at a temperature of 60°C and 0.1 bar to dry for 48 hours.

[0090] Step 2: fully mixing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers in a solvent to obtain a mixed slurry; the mass ratio of the mica nanosheets, fluorinated graphene and meta-nano-aramid fibers is 0.1-0.3:0.1-0.2:1;

[0091] The preparation process of mica nanosheets is as follows:

[0092] Weigh 1g of anhydrous lithium citrate as an intercalant and stir thoroughly in 60g of deionized water until completely dissolved. Add 1g of natural mica powder with an average particle size of 20μm and 40g of isopropyl alcohol to the lithium citrate aqueous solution;

[0093] Then, the mixture was placed under 200W, 40kHz water bath ultrasound for 30 minutes to obtain a uniformly dispersed mica dispersion. The mica dispersion was poured into a hydrothermal reactor lined with polytetrafluoroethylene and hydrothermally reacted at 100°C for 6 hours.

[0094] After the hydrothermal reaction is completed, the peeled mica nanosheets are poured out of the hydrothermal reactor and centrifuged and rinsed at least 5 times with 50 mL of deionized water at 2000-25000 rpm each time. The rinsed mica nanosheet powder is placed in a vacuum environment of 60° C. and 0.1 bar and dried for 72 hours.

[0095] The preparation process of meta-nano-aramid fiber is as follows:

[0096] Meta-aramid fiber filaments were mechanically sheared into chopped fibers with a length of 5 to 10 mm. The chopped fibers were then soaked in acetone and subjected to 300W waterbath sonication for 72 hours to remove stains. After the acetone was filtered off, the chopped fibers were soaked in anhydrous ethanol for 12 hours. The fibers were then vacuum-filtered and rinsed three times with anhydrous ethanol and then with deionized water. The rinsed fibers were vacuum-dried at 60°C for at least 5 days before use.

[0097] Weigh 4.8g of KOH into a brown, wire-top bottle. Add approximately 20mL of deionized water and stir until the KOH is completely dissolved. Then, add 1000mL of DMSO and mix thoroughly to create a concentrated DMSO solution. Finally, add 3.2g of pretreated meta-aramid fiber to the concentrated DMSO solution. Seal the bottle and stir at 800rpm in the dark at 20°C for 7 days to obtain a dark red nano-aramid fiber dispersion.

[0098] Take 620mL of DMSO solvent, add 0.15g of mica nanosheets and 0.1g of fluorinated graphene, and ultrasonicate in a water bath for 30 minutes; then add 310mL of nano-aramid fiber dispersion; drop 10mL of deionized water into the mixed solution, ultrasonicate in a water bath for 3h, and then quickly inject the prepared mixed solution into 1000mL of deionized water to generate a flocculent liquid; repeatedly wash the flocculent with a Buchner funnel, filter out the residual solvent, disperse the flocculent in 500mL of deionized water and high-speed shear at a speed of 12000rpm for 20min to obtain a dispersed and stable slurry as the outer layer material.

[0099] Step 3: preparing a nanofiber mat using the coaxial nanofibers obtained in step 1;

[0100] Step 4: Using the nanofiber mat obtained in step 3 as the interlayer material and the mixed slurry as the surface material, a multilayer structure material is formed by vacuum filtration, wherein the upper and lower surfaces of the interlayer material are covered with the surface material;

[0101] Measure an appropriate amount of the outer layer material from step 2 so that the ratio of outer layer material to interlayer material is 8:2. Divide the outer layer material slurry into two equal portions. Pour either portion of the outer layer material slurry into a filtration flask. Using the nanofiber felt obtained in step 3 as a filter membrane, vacuum filter the outer layer material slurry in the filtration flask until it is dry and the solids in the slurry are completely deposited on the filter membrane surface. Then, turn the composite nanofiber felt filter membrane over and filter the other portion of the outer layer material using the same method until dry. This will yield a multilayer structure material.

[0102] Step 5: hot-press the multilayer structure material obtained in step 4 to obtain the desired composite aramid insulation paper.

[0103] The multilayer structure material obtained in step 4 is placed in the pressure plate of the hot press, and the hot pressing pressure is set to 12 MPa; during the hot pressing process, first hot press at 180°C for 6 minutes, then return to room temperature and cold press for 2 minutes to obtain the required composite aramid insulation paper.

[0104] Example 2

[0105] The other steps of this embodiment are the same as those of embodiment 1, except that in step 4, the quantitative ratio of the outer layer material to the interlayer material is 9:1.

[0106] Example 3

[0107] The other steps of this embodiment are the same as those of embodiment 1, except that in step 4, the quantitative ratio of the outer layer material to the interlayer material is 7:3.

[0108] Example 4

[0109] The other steps of this embodiment are the same as those of Example 1, except that in step 2, the masses of the mica nanosheets and the fluorinated graphene are 0.3 g and 0.15 g, respectively.

[0110] Example 5

[0111] The other steps of this embodiment are the same as those of Example 1, except that in step 2, the masses of the mica nanosheets and the fluorinated graphene are 0.2 g and 0.2 g, respectively.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 1 is that step 1 is not included, and the process of step 3 is as follows: 620 mL of DMSO solvent was added thereto, 0.30 g of carbon nanotubes was added thereto, and water bath sonication was performed for 30 min. Then, 310 mL of the nano-aramid fiber dispersion prepared in step 2 of Example 1 was added thereto, and then 10 mL of deionized water was dropwise added to the mixed solution, and water bath sonication was performed for 3 h. Subsequently, the prepared mixed solution was rapidly injected into 1000 mL of deionized water to generate a flocculent solution. The flocculent was repeatedly washed with a Buchner funnel to filter out residual solvent, and the flocculent was dispersed in 500 mL of deionized water and sheared at a speed of 12000 rpm for 20 min to obtain a dispersed and stable mixed slurry. Finally, the mixed slurry was vacuum filtered with a polytetrafluoroethylene filter membrane to dryness, and the filter membrane was removed to obtain a sandwich material.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 1 is that step 1 is not included, and step 3 uses aluminum foil with a thickness of 10 μm as the interlayer material, supplemented by an adhesive.

[0116] The specific preparation process of step 4 is as follows:

[0117] Take two portions of the outer layer material slurry exactly the same as in step 4 of Example 1, and vacuum filter them with a polytetrafluoroethylene filter membrane until the slurry is completely dry. After removing the filter membrane, two sheets of outer layer material of the composite insulating paper are obtained. The aluminum foil as the interlayer material is cut to make it consistent with the shape of the outer layer material, and an acrylic adhesive is evenly coated on both sides. Then, the two sheets of outer layer material are respectively bonded to the two sides of the interlayer material, and after hot pressing, the composite aramid insulating paper of this comparative example is obtained.

[0118] Comparative Example 3

[0119] The difference between this comparative example and Example 1 is that mica nanosheets and fluorinated graphene are not included in step 2.

[0120] The performance of the insulating paper obtained in the above embodiment is tested as follows:

[0121] The corona resistance performance test method refers to the current national standard GB / T 22689-2008 "Recommended test method for determining the relative resistance of solid insulating materials to surface discharge breakdown" to conduct thermal aging high-frequency pulse corona resistance duration test.

[0122] The puncture strength and tensile strength tests are carried out in accordance with GB / T 20629.2-2013 "Non-cellulose paper for electrical purposes Part 2: Test methods"; the electromagnetic shielding effect test of composite insulating paper is based on GB / T 30142-2013 "Measurement method of shielding effectiveness of planar electromagnetic shielding materials".

[0123] from Figure 4and Figure 5 Test results show that the insulating paper obtained in Example 1 of the present invention exhibits superior partial discharge resistance, with significantly better breakdown strength and corona resistance time than the comparative example. The superior breakdown strength of Example 1 compared to Comparative Examples 1 and 2 is due to the coaxial nanofibers in the interlayer material of the present invention being made of aramid fibers, while Comparative Example 1 uses exposed highly conductive carbon nanotubes and Comparative Example 2 uses aluminum foil. Compared to Example 1 and Comparative Example 3, the nanofunctional fillers in the outer layer material of the present invention effectively hinder the formation and development of discharge channels.

[0124] from Figure 6 It can be seen from the electromagnetic shielding results that compared with the insulating paper obtained in the comparative example, the electromagnetic shielding performance of the insulating paper obtained by the present invention is significantly superior. It can be seen that a carbon nanotube nanoconductive network with excellent electromagnetic shielding performance is constructed in the interlayer material.

[0125] from Figure 7 It can be seen that the thermal conductivity of the insulating paper obtained in Example 1 of the present invention is higher than that in Comparative Examples 1 and 2. The thermal conductivity of the insulating paper obtained in Example 1 is 5.44 W·m -1 K -1 , which is about 1.97 times that of Comparative Example 3. The outer layer material in the present invention comprises highly thermally conductive fluorinated graphene and mica nanosheets.

[0126] from Figure 8 It can be seen that the insulating paper obtained by the present invention can withstand stronger mechanical stress than the aluminum foil interlayer in Comparative Example 2. This is because the similar interface characteristics between the layers of material make their connection tighter.

[0127] The present invention uses a nanofiber mat composed of coaxial nanofibers with meta-aramid fibers as the shell and carbon nanotubes as the core as the interlayer material. During heat pressing (12 MPa, 180°C), the high-molecular-weight aramid fibers in the coaxial fiber shell soften or melt, and the highly conductive and heat-resistant carbon nanotubes in the core are mechanically squeezed into contact. After returning to normal temperature and pressure, a layered network structure is formed with external electrical insulation and a highly conductive interior. Compared with existing traditional electromagnetic shielding media such as aluminum foil and silver nanowire mesh, the insulating paper obtained by this invention does not sacrifice the insulating properties of the insulating paper, resulting in excellent electromagnetic shielding performance.

[0128] The insulating paper obtained by the present invention uses fluorinated graphene with a particle size of 4 to 8 μm and a thickness of 1 to 2 mm and mica nanosheets with a particle size of 300 to 600 nm and a thickness of 100 to 200 nm as synergistic nanofillers in the outer layer material. Graphene fluoride can significantly improve the thermal conductivity of the insulating paper, and its strong electrical insulation properties help to enhance the insulation strength of the insulating paper. Mica nanosheets have outstanding resistance to partial discharge (corona), and their selection as anti-corona functional elements can significantly extend the anti-corona time of the insulating paper. More importantly, under the vertical attraction of the vacuum filtration preparation process, these two nanomaterials can achieve a reasonable "size matching" stacking due to the significant differences in particle size and thickness, thereby constructing a denser composite structure in the outer layer material of the composite insulating paper. This combination of nanoparticles of different sizes can not only effectively fill the gaps between traditional single nanofiller particles and improve the density of the material, but also form a nested structure, which helps to hinder the generation and development of discharge channels, further improving the insulation, thermal conductivity and other properties of the insulating paper.

[0129] The outer layer material is composed of aramid nanofibers, mica nanosheets, and fluorinated graphene, wherein the aramid nanofibers are high molecular polymers, the mica nanosheets are aluminum silicate minerals, and the fluorinated graphene is a carbon derivative. The three nanomaterials with different properties and physical scales are stacked and contacted with each other, forming three interfaces in the outer layer material. Due to the large number of microscopic defects on the surface of the nanoparticles, rich deep traps can be introduced between different interfaces. The deep traps can capture charge carriers and hinder their migration, while forming a shielding electric field in the opposite direction of the applied electric field of the material, thereby improving the breakdown resistance and corona resistance of the insulating paper. The present invention adopts mica nanosheets to cooperate with fluorinated graphene to dope the aramid nanofibers of the outer layer material. While achieving reasonable stacking and constructing a dense structure, it also introduces rich interfaces and a large number of deep traps into the outer layer material, playing a role in improving the insulation and corona resistance of the composite insulating paper.

[0130] The insulating paper of the present invention uses a vacuum filtration-assisted high-temperature hot pressing process to tightly bond the interlayer material to the outer layer material, eliminating the need for any adhesives. This eliminates the insulation risk of aging and peeling of the adhesive between the electromagnetic shielding layer and the insulating paper substrate, common in conventional electromagnetic shielding insulating paper. Furthermore, the interlayer and outer layer materials of the composite aramid insulating paper provided by the present invention are both primarily made of nano-aramid fibers, resulting in consistent interface properties and high affinity, which contributes to the formation of a tightly bonded composite insulating paper. Compared to conventional multi-layer electromagnetic shielding insulating paper, its operating life is significantly increased, and the probability of aging and delamination failures is greatly reduced.

[0131] The composite aramid insulation paper produced by the present invention has excellent electromagnetic shielding performance, while also offering advantages such as high electrical strength, long corona resistance, and mechanical stress resistance. It can address the shortcomings and issues of conventional electromagnetic shielding insulation papers, such as those with aluminum foil interlayers, in terms of breakdown strength and corona resistance, and is well-suited to the development needs of advanced power electronic devices and electrical equipment.

Claims

1. A method for preparing high thermal conductivity corona resistant electromagnetic shielding composite aramid insulation paper, characterized in that: The following steps are involved: Step 1: Using meta-aramid fiber as the shell layer and carbon nanotubes as the core layer, coaxial nanofiber filaments are obtained by coaxial electrospinning; Step 2: fully mixing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers in a solvent to obtain a mixed slurry; the mass ratio of the mica nanosheets, fluorinated graphene and meta-nano-aramid fibers is 0.1-0.3:0.1-0.2:1; Step 3: preparing a nanofiber mat using the coaxial nanofibers obtained in step 1; Step 4: Using the nanofiber mat obtained in step 3 as the interlayer material and the mixed slurry as the surface material, a multilayer structure material is formed by vacuum filtration, wherein the upper and lower surfaces of the interlayer material are covered with the surface material; Step 5: hot-press the multilayer structure material obtained in step 4 to obtain the desired composite aramid insulation paper.

2. The method for preparing a high thermal conductivity and corona resistant electromagnetic shielding composite aramid insulation paper according to claim 1, characterized in that: In the step 1, the diameter of the coaxial nanofiber filament is 200-600 nm, and the ratio of the radius of the core layer to the thickness of the shell layer in the coaxial nanofiber filament is 2-5:8-5.

3. The method for preparing a high thermal conductivity and corona resistant electromagnetic shielding composite aramid insulation paper according to claim 1, characterized in that: The intermediate aramid fiber in step 1 needs to be pretreated before use: Cutting the meta-aramid fiber into 5-10 mm short fibers; The chopped fibers were ultrasonically treated in acetone, then vacuum filtered and rinsed three times, and then dried. After drying, the fibers were dissolved in a LiCl solution to obtain a meta-aramid fiber solution.

4. The method for preparing a high thermal conductivity and corona resistant electromagnetic shielding composite aramid insulation paper according to claim 1, characterized in that: The preparation method of the mica nanosheets in step 2 is as follows: adding mica powder to the intercalant solution and obtaining a mica dispersion after ultrasonication; The mica dispersion was heated at 100°C for 6 hours; after centrifugal rinsing, it was dried under vacuum conditions; The preparation process of meta-nano-aramid fiber is as follows: Cutting the meta-aramid fiber into 5-10 mm short fibers; The chopped fibers were ultrasonicated in acetone, then rinsed three times by vacuum filtration and then dried; The dried meta-aramid fiber is dissolved in a strong alkaline solution, fully stirred, and subjected to ultrasonic dispersion treatment.

5. The method for preparing a high thermal conductivity and corona resistant electromagnetic shielding composite aramid insulation paper according to claim 1, characterized in that: The mixed slurry preparation process in step 2 is as follows: Mica nanosheets and fluorinated graphene were added to the solvent dimethyl sulfoxide and ultrasonicated in a water bath; adding meta-nano-aramid fiber dispersion; Deionized water is dropped into the mixed solution, and the mixture is subjected to water bath ultrasonic treatment to obtain a mixed solution; The mixed solution after ultrasonication was injected into deionized water to generate floccules; The flocculants are dispersed in deionized water and sheared at high speed to obtain a dispersed and stable mixed slurry.

6. The method for preparing a high thermal conductivity, corona-resistant, electromagnetic shielding composite aramid insulation paper according to claim 1, characterized in that: In step 4, the mass ratio of the surface layer material to the interlayer material is 7-9:3-1.

7. The method for preparing a high thermal conductivity, corona-resistant, electromagnetic shielding composite aramid insulation paper according to claim 1, characterized in that: The hot pressing process in step 5 is as follows: First, hot pressing was performed at a pressure of 12 MPa and a temperature of 180°C for 6 min; Then, the pressure was maintained at 12 MPa at room temperature for 2 minutes.

8. The high thermal conductivity, corona resistance, electromagnetic shielding composite aramid insulation paper obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The composite aramid insulation paper is a composite sandwich structure formed by hot pressing with the upper and lower surfaces of the sandwich material covered with the outer layer material; The sandwich material is a composite nanofiber felt prepared by coaxial nanofiber filaments obtained by coaxial electrospinning, with meta-aramid fiber as the shell layer and carbon nanotubes as the core layer; The outer layer material is a mixed slurry obtained by fully mixing and dispersing mica nanosheets, fluorinated graphene and meta-nano-aramid fibers.

9. The high thermal conductivity and corona resistance electromagnetic shielding composite aramid insulation paper according to claim 8, characterized in that: The carbon nanotubes have a length of 0.4 to 5 μm and a diameter of 8 to 20 nm; the mica nanosheets have a particle size of 300 to 600 nm and a thickness of 100 to 200 nm; the fluorinated graphene has a single-layer structure, a fluorine-carbon ratio of 1:1, a particle size of 4 to 8 μm, and a thickness of 1 to 2 nm.

10. The use of the high thermal conductivity, corona resistance and electromagnetic shielding composite aramid insulation paper according to any one of claims 8 to 9, characterized in that: The composite aramid insulation paper is used for preparing insulation components of power transformers.

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